The invention relates to a mould for the casting of hollow products or products with recesses and made of a plastic which quickly expands after deforming, which mould includes two mould parts and a one piece core surrounded thereby, whereby the mould, parts and the core for injection moulding of the plastic enclose a mould cavity provided with filling channels. The invention further relates to a preferred use of such a mould.
A mould of this type is illustrated in FIGS. 6 and 7 of the EP 0 002 311 and briefly described in the reference. This mould serves the production of a bellows including recesses. The mould consists of two mould parts which surround a core. It is described in the reference that the material placed in the mould quickly expands after opening of the mould and thereby releases the core.
Such expanding plastics, especially EVA (ethylene/vinyl acetate copolymer) are used more recently more often for different articles, for example shoe soles. The EVA material is a closed cell foam from which water proof, non-toxic, differently colored products with good technical properties can be made. These products are mostly formed by injection moulding. After the injection moulding and after opening of the mould, the material expands almost immediately by 20 to 80%. It is therefore required that the products are quickly removed from the mould so that an even expansion of the products is guaranteed and so that they cannot deform because of contact with mould parts. This has resulted in the products currently on the market having a simple shape, without hollow spaces and recesses, for example shoe, soles.
One-piece shoes of other plastic, materials such as for example polyurethane, thermoplastics and PVC are also known. Such shoes however do not have the advantageous properties which can be achieved with EVA.
Purposes of the Invention
It is an object of the invention to provide a mould of the above mentioned general type but further adapted for the manufacture of products with recesses, especially footwear with sole and shaft, wherein the danger of deformation of the products immediately after removal from the mould by expansion of the product is as small as possible and which permits injection moulding in a single injection step.
It is a further object of the invention to provide an advantageous use for the mould of the invention.
The first object is achieved in accordance with the invention in that the core within the mould has an extension and rests with that extension against both mould parts, that the extension is held en a guide column to be movable out of the respective mould part when the mould is opened, and that a compression spring is provided in one of the mould parts which is supported on the mould part and the core for quickly forcing the core out of the mould parts when the mould is opened.
With such a mould it is sufficient for the opening of the mould to lift one mould part off the other. The core and the injection moulded product surrounding it are thereby together quickly removed from the two mould parts by the pressure spring so that an expansion of the moulded part outside the mould is achieved preventing deformations caused by contact with the mould parts. Thus, high-quality, products of EVA including cavities and recesses can be produced with the invention without deformation, for example shoes, bags or portfolios.
The shaft of shoes often requires through-holes to provide for a better aeration of the foot. So far, such shoes with through-holes in the shaft could only he manufactured with complex moulds which include pins of a diameter corresponding to the, one of the de holes. These pins must be inserted into the mould before the injection moulding and again removed before removal of the shoe from the mould. However, that resulted in undesirably high manufacturing costs. These known moulds would be useless for the manufacture of shoes with through-holes when materials are used which are fast foaming and expand after removal. from the mould.
Shoes or other products with lateral through-holes can be manufactured in a simple, fast and cost efficient manner with an advantageous preferred embodiment in accordance with the invention wherein the core has protruding cams which bridge the cavity in the two mould parts.
The removal of the expanded shoe from the mould is especially easily achieved when the maximum radial extent of the cams is no larger than the inner dimension of the expanded product.
The mould is of especially simple construction when the cams are clamped into lateral recesses of the closed mould.
The second object of the invention, namely the finding of an advantageous use for the mould in accordance with the invention, is achieved in accordance with the invention in that the mould is used for the injection moulding of hollow products made of EVA material.